Inkjet printers are well known in the art. Small droplets of liquid ink, propelled by thermal heating, piezoelectric actuators, or some other mechanism, are deposited by a printhead on a print media, such as paper. By depositing a succession of drops on the print media, text and images are formed.
Inkjet printheads, or “pens”, are typically manufactured in a manner similar to the manufacture of semiconductor integrated circuits. The ink ejection mechanisms, or “nozzles”, are typically formed in a linear array, with ink feed paths formed through the printhead to provide the nozzles with ink. A limitation on the print speed for a given printhead design is the rate at which successive drops can be “fired” from a nozzle, which is primarily determined by the fluid refill time of the ink ejection mechanism.
Inkjet pens are complex mechanisms. The rapid refill of the nozzle firing chambers involves factors such as the momentum of the ink, surface tension, and the geometry of the fluidic channels. A given inkjet pen design may work well at some points within its operating range and less well at others. The printhead design may, for example, be optimized such that there are broad “resonances” in the ink channels and firing chambers that may be advantageous to the rapid refill of the firing chambers, but which have adverse affects under some conditions. A design that is optimized to provide a high maximum firing rate (and thus a fast print speed) may produce a poor print quality or prove unreliable at slower, non-optimum print rates.
One problem sometimes encountered is termed “puddling”, where the geometry of the ink refill paths and the momentum of the ink flowing through the paths cause ink to spill out of the firing chambers and onto the printhead orifice plate. The presence of the “puddles” on the orifice plate can cause ink drops fired from nearby firing chambers to land off target, and other printing problems.
In scanning-carriage inkjet printing systems, such are typically used in homes and offices, inkjet printheads are typically mounted on a carriage that is moved back and forth across the print media. As the printheads are moved across the print media, a control system activates the printheads to deposit or eject ink droplets onto the print media to form text and images. The print media is generally held substantially stationary while the printheads complete a “print swath”; the print media is then advanced between print swaths. Because scanning carriage systems can control all facets of the printing process, including the pen firing rate, the carriage speed across the media, and the paper advance rate, the printers can be designed with defined print modes that avoid any problematic areas in the printhead operating range.
In many industrial applications, such as the printing of labels or barcodes on a production line, the required printing rate may be dictated by external factors other than the preferred operating point of the printhead, such as, for example, the rate at which items progress down the production line. In such applications, it is advantageous that the printer be able to print acceptably at whatever rate is required by the external factors. It is also economically desirable to be able to utilize existing, readily-available inkjet pens in many industrial applications, rather than specialized, high cost designs.
There is thus a need for methods that allow an industrial inkjet printer pens to adaptably print at various rates while avoiding areas of poor performance.